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Peer Review Report on Global Precipitation Enhancement Activities

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Peer Review Report on Global Precipitation Enhancement Activities WWRP 2018 - 1 Peer Review Report on Global Precipitation Enhancement Activities Authors: Andrea I. Flossmann, Michael Manton, Ali Abshaev, Roelof Bruintjes, Masataka Murakami, Thara Prabhakaran and Zhanyu Yao Reviewers: Zev Levin, Steven Siems and 2 anonymous reviewers EDITORIAL NOTE METEOTERM, the WMO terminology database, may be consulted at: http://www.wmo.int/pages/prog/lsp/meteoterm_wmo_en.html. Acronyms may also be found at: http://www.wmo.int/pages/themes/acronyms/index_en.html. © World Meteorological Organization, 2018 The right of publication in print, electronic and any other form and in any language is reserved by WMO. Short extracts from WMO publications may be reproduced without authorization, provided that the complete source is clearly indicated. Editorial correspondence and requests to publish, reproduce or translate this publication in part or in whole should be addressed to: Chairperson, Publications Board World Meteorological Organization (WMO) 7 bis, avenue de la Paix Tel.: +41 (0) 22 730 84 03 P.O. Box 2300 Fax: +41 (0) 22 730 80 40 CH-1211 Geneva 2, Switzerland E-mail: [email protected] NOTE The designations employed in WMO publications and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of WMO concerning the legal status of any country, territory, city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. The mention of specific companies or products does not imply that they are endorsed or recommended by WMO in preference to others of a similar nature which are not mentioned or advertised. The findings, interpretations and conclusions expressed in WMO publications with named authors are those of the authors alone and do not necessarily reflect those of WMO or its Members. This publication has been issued without formal editing. CONTENTS EXECUTIVE SUMMARY .................................................................................................... iii 1. INTRODUCTION ................................................................................................... 1 2. NATURAL CLOUD SYSTEMS AND THEIR VARIABILITY ................................................ 5 2.1 General introduction ........................................................................................................... 5 2.2 Formation of clouds and the role of aerosol particles ............................................................... 5 2.2.1 Formation of drops on cloud condensation nuclei (CCN) ................................................ 7 2.2.2 Formation of ice crystals on ice nucleating particles (INP) ............................................. 7 2.3 Cloud microphysics ............................................................................................................ 10 2.3.1 Growth of cloud particles .......................................................................................... 10 2.3.2 Electrical processes in cloud ...................................................................................... 12 2.4 Cloud systems of interest in weather modification ................................................................. 13 2.4.1 Introduction ........................................................................................................... 13 2.4.2 Wintertime orographic cloud systems ......................................................................... 13 2.4.3 Convective cloud systems ......................................................................................... 14 2.5 Conclusions ....................................................................................................................... 16 3. POTENTIAL FOR PRECIPITATION ENHANCEMENT ...................................................... 17 3.1 Introduction ...................................................................................................................... 17 3.2 Winter orographic clouds .................................................................................................... 17 3.2.1 Physical basis of seeding winter orographic clouds ....................................................... 17 3.2.2 Seeding strategies ................................................................................................... 20 3.2.3 Snow chemistry ...................................................................................................... 21 3.3 Convective and stratiform cloud systems .............................................................................. 22 3.3.1 Physical basis of seeding convective cloud systems ...................................................... 24 3.3.1.1 Hygroscopic seeding ................................................................................... 24 3.3.1.2 Glaciogenic seeding .................................................................................... 25 3.3.2 Seeding strategies ................................................................................................... 25 3.3.2.1 Seeding methods ....................................................................................... 25 3.3.2.2 Seeding materials ...................................................................................... 26 3.3.2.3 Transport and dispersion ............................................................................. 28 3.3.2.4 Tracer releases .......................................................................................... 29 3.4 Redistribution and “negative enhancement” of precipitation .................................................... 30 3.5 Alternative technologies ...................................................................................................... 32 3.5.1 Ionization ............................................................................................................... 32 3.5.2 Electric fields and modification of electricity ................................................................ 33 3.5.3 Laser technologies ................................................................................................... 33 3.5.4 Acoustic waves ....................................................................................................... 34 3.6 Conclusions and recommendations ....................................................................................... 34 4. OBSERVATIONS OF AEROSOL, CLOUDS AND PRECIPITATION ..................................... 36 4.1 Introduction ...................................................................................................................... 36 4.2 Observations of precipitation ............................................................................................... 36 4.2.1 Ground-based rain and snow observations .................................................................. 36 4.2.2 Ground-based radar observations .............................................................................. 37 4.2.3 Space-borne observations ........................................................................................ 38 4.3 Observation of the synoptic environment .............................................................................. 39 4.4 Observations of cloud dynamics ........................................................................................... 40 4.5 Aerosol and cloud microphysics measurements ...................................................................... 41 4.5.1 Microphysics ........................................................................................................... 41 4.5.2 Supercooled liquid water (SLW) ................................................................................ 42 4.5.3 Satellite observations .............................................................................................. 42 4.5.4 Aerosol particles ..................................................................................................... 43 4.5.5 Ice nucleating particles (INP) .................................................................................... 43 4.5.6 Snow physics .......................................................................................................... 44 4.5.7 Emerging technology ............................................................................................... 44 4.6 Laboratory measurements .................................................................................................. 44 4.7 Conclusions ...................................................................................................................... 45 5. MODELLING OF NATURAL CLOUDS AND SEEDED CLOUDS ......................................... 47 5.1 Introduction ...................................................................................................................... 47 5.2 Numerical models used in weather modification ..................................................................... 47 5.2.1 Types of model frameworks ...................................................................................... 47 5.2.2 Cloud microphysics .................................................................................................. 49 5.2.3 Seeding schemes .................................................................................................... 50 5.3 Hygroscopic seeding ........................................................................................................... 51 5.3.1 Model studies using simplified
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